Underpowered Amplifier Need Guidance - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 16 Old 07-30-15, 10:27 PM Thread Starter
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Underpowered Amplifier Need Guidance

So I'm new to these forums and I'm not sure if this is a stupid question or not. So I have two floor PA speakers, (WELTON AUDIO PS412-1 TOWER SPEAKER). They have a rating of 150 W NOM (I'm assuming RMS) and 400 W max. I currently have them running them through aa Adcom GFA-535 II preamp which is rated at 60 W RMS. I wanted to upgrade to a more powerful amp so I purchased the musysic sys-2000 amp which is rated at 250 W RMS at 8 Ohms (which I'm assuming is the resistance of the PA speakers. According to these numbers I was under the impression that the new preamp would blow the Adcom out of the water. However after comparing the two preamps, the adcom is by far louder and cleaner than the musysic amp. What am I missing here? And if I did want to power my speakers effectively would preamp would you recommend? I can't post any links to the items i own since I'm a new member hope you guys can help out.
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post #2 of 16 Old 07-31-15, 09:27 AM
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Re: Underpowered Amplifier Need Guidance

Welcome to the Forum bobcat!

First, The Adcom and Musysic are amplifiers, not preamplifiers.

Second, I assume you had the gain knobs on the Musysic amp all the way up?

Nevertheless, it stretches the imagination that a $100 amplifier can really put out a true and clean 250 watts RMS per channel. That Adcom amp cost $300 twenty-five years ago. What is that, over $500 today? A good clue is that Musysic's web site does not qualify what the distortion level (THD) is at 250 watts, nor at what frequency or frequency range, as you find with most good home audio amplifiers.

For example, compare the power specs of this amplifier from Yamaha:
Rated Output Power (20Hz – 20 kHz, 2 channels driven): 150 W (8 ohms @ .06% THD)
Rated Output Power (1 kHz, 1 channel driven): 190 W (8 ohms @.09 THD)

You can see from this that the way the amplifier is rated makes a difference. With only one channel driven, and at a single frequency (1 kHz), the amp puts out “more” power. A broadband signal (20 Hz – 20 kHz) generated with both channels driven is a much more demanding (and I might add, real-world) situation. Subsequently the power output is less, but more realistic as no one listens to 1 kHz sine waves.

Now look at the power specs of the Musysic amp:
250 W @ 8 ohms

As you can see, this spec has absolutely no relevance: Was it generated at a single frequency or broadband? Single or both channels driven? What is the THD at 250 watts? After all, clean power is all that matters. Any amp is capable of delivering tremendous peak wattage if you can live with distortion that makes your ears bleed.

Note that the Musycic amp does have a separate THD rating of 0.1%, which is a respectable figure, but there is no indication at what power output that it exhibits that rating. For all we know the amp could be generating 20% distortion at 250 watts.

Bottom line, at the end of the day it’s very likely that your two amps are not that different in power outputs, as Adcom adheres to the same specification standards shown in the Yamaha example above, and indeed had a reputation for underrating their amplifier power.

Nevertheless, power ratings don't matter so much as whether or not you're able to play the system as loud as you want to. If the Adcom can do that, then there was no reason to buy the Musysic amp to begin with.

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post #3 of 16 Old 07-31-15, 09:46 AM
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Re: Underpowered Amplifier Need Guidance

^^^Agree. The specs for the Musysic amp aren't very clear and lead me to suspect they aren't as they appear.
For a little bit more money, the lesser Crown and some QSC amps are a lot of bang for the buck.

The Crown XLS and XLi series seem to be good performers and have decent specs.
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post #4 of 16 Old 07-31-15, 10:34 AM Thread Starter
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Re: Underpowered Amplifier Need Guidance

Thank you for your help! I should've assumed the musysic amp wouldn't have done the job properly and wasn't sure how to interpret some of the specs it gave.

With that being said I would like my system to get louder before my speakers start to clip. Right now I'm looking at the crown XLS-1000 which I know is a reliable brand.

Thanks again guys I really appreciate it!
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post #5 of 16 Old 07-31-15, 10:55 AM
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Re: Underpowered Amplifier Need Guidance

Check out the Yamaha Pro amps too... excellent build quality, sound great, and usually zero fan noise.


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post #6 of 16 Old 07-31-15, 11:12 AM
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Re: Underpowered Amplifier Need Guidance

I agree with the above post for sure but here is another option. B+H photo is selling Crowns for a great price and the XLS-2000 would be all the amp you need for a great price. Check it out ...http://www.google.com/aclk?sa=l&ai=C...LS2000%26m%3DY

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post #7 of 16 Old 07-31-15, 11:43 AM Thread Starter
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Re: Underpowered Amplifier Need Guidance

Yes I was considering the XLS 2000 as well. I found a great local deal on a new XLS 1000 for 150 though so I don't think I can pass that up.
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post #8 of 16 Old 07-31-15, 03:12 PM
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Re: Underpowered Amplifier Need Guidance

I own the Crown XLC2500, I preferred the XLC over the XLS because the XLC is a class AB amp and the XLS is a Class D. The XLC also has the ability to change the input sensitivity
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post #9 of 16 Old 08-01-15, 11:04 AM
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tcarcio wrote: View Post
I agree with the above post for sure but here is another option. B+H photo is selling Crowns for a great price and the XLS-2000 would be all the amp you need for a great price. Check it out ...http://www.google.com/aclk?sa=l&ai=C...LS2000%26m%3DY
Thanks for the link, that is a good price.
As far as pro amps go this one is about as home audio friendly as they get with the inclusion of RCA jacks and speaker terminals.
Do you have any additional information on the >.5% THD spec ?
It's kinda open ended being greater than vs less than.
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post #10 of 16 Old 08-01-15, 11:47 AM
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Re: Underpowered Amplifier Need Guidance

Also look at the Samson servo http://www.bhphotovideo.com/c/produc...300_Power.html at B&H I have one of theses and two of the servo 600 amps. They also have rca inputs.

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